For many injection devices intended for self-administration of medicament, it is often desirable that the device is as complete as possible, i.e. that the number of operations or assembly steps needed in order to make the device ready to deliver a dose of medicament is minimized.
One solution for keeping a medicament delivery device as pre-assembled as possible is to deliver the medicament delivery device with a delivery member, such as a needle, pre-attached. This solution often causes the rear end of the needle to protrude into the interior of the container, which could be a drawback if the medicament reacts with the material of the delivery member when exposed for a period of time. In that respect it would be desirable to have the rear part of the delivery member outside the container until the delivery is to be performed.
On the other hand, the front part of the delivery member has to be protected before use in order to prevent unintentional needle sticks and in order to keep the needle clean. The front end of the delivery member is therefore often arranged with a sheath and/or a cap that has to be removed beforehand.
In order to accomplish the above in a simple and effective way, the applicant has developed a cap assembly that comprises a retainer member connectable to a medicament container holder of a medicament delivery device. The cap assembly further comprises a hub coaxially movable within the retainer member where the hub comprises a needle having a proximal end and a distal end. An inner cap is interactively connected to the hub and the retainer member. The engagement between the outer cap and the inner cap and between the inner cap and the retainer member is configured such that removal of the outer cap causes the hub to move distally such that the distal end of the needle penetrates the proximal end of the medicament container.
For some types of medicament to be delivered, that are contained in a medicament container placed inside the medicament delivery device, there is a tendency that pressure can build up inside the container, which pressure could be considerable. When a cap assembly like the one described above then is operated for removing it and the distal end of the needle penetrates the medicament container, the over-pressure is relieved through the needle.
If the device is held correctly with the proximal end of the injection needle pointing substantially vertical upwards, then mostly air will be relieved through the needle during de-aeration. However, if the device is tilted and is held more horizontally, then amounts of medicament will be expelled through the needle when the over-pressure is relieved.
This is a drawback in many ways. If the medicament container comprises a certain prescribed dose volume to be delivered to a patient, then unintentional expelling of a volume during removal of the cap assembly will lead to an inferior dose quantity being delivered during the subsequent injection. If a multi-dose container is used, then the last dose to be delivered will be of inferior volume. This may be serious for drugs requiring certain rather specific dose volumes in order to give adequate treatment. Also, the mere uncontrolled expelling of a drug volume into the environment is a hazzle and an inconvenience.
Some solutions have been presented for ascertaining that medicament delivery devices are held in a proper position during certain handling steps. For example, the document WO 2007/099044 discloses a medicament delivery device, which is arranged to handle a multi-chamber medicament container. In order to ascertain that the device is held in the proper vertical position during the priming of the multi-chamber container after a mixing operation, a direction sensitive mechanical solution is presented, which can comprise a ball that may be moved from an engagement position, enabling priming, to a disengagement position where no priming may be performed. In the engagement position, it is possible to manually push a priming sleeve such that a pre-tensioned plunger rod is released a certain predetermined distance such that the medicament container is primed by expelling entrapped air.
This solution is rather complicated since the design is built into the device, adding costly features to the design. Also WO 2007/099044 only deals with the situation during priming after mixing of a multi-chamber container. The solution comprises a number of features and interacting components. Further, the document does not deal with the situation when the inner of a medicament container is suddenly in communication with the surrounding by a penetrating needle during removal of the cap assembly.